172 NAVICULA. 



space round the raphe, diminishing in length on nearing the central 

 nodule around which they are completely absent, thus producing a pseudo- 

 stauros ; about 10 to 12 in 1 c.d.m. Length of valve, about ioc.d.m. 



Fresh water. Eegenhoven near Louvain (P. Gaut. ), etc., France. 



Var. parva. (Stauroptera parva Ehr. H.V.H. Atl. pi. 6, f. 6*) plate 

 2, fig. 86. 



Distinguished from the preceding by its smaller size (about 6 to 

 7 c.d.m.) and its median portion being more inflated. 



Ditches near Nieuport (Westendorp and Wallays according to Rabenhorst : Fl. Eur. 

 Alg. , p. 222). 



N. Tabellaria Ehr. (Verb., p. 134, pi. II i., f. 26 ; Kiitz. Bac. p. 

 98, pi. 28, f. 79 ; H.V.H. Atl., pi. 6, f. 8*), plate 2. fig. 87. 



Differs from the preceding by the terminal and median inflations being 

 much more marked, by the costse occupying all or nearly all the valve, but 

 reduced almost to dots at the exact median portion, their number being more 

 considerable, 12 to 15 in 1 c.d.m., and lastly by its more considerable size, 

 which attains to 14 c.d.m. 



The terminal costse have been designated radiate in error, they are con- 

 vergent, as in the preceding species. 



Fresh water. Eegenhoven near Louvain (P. Gaut.). England, France. Mixed with the 

 preceding and the following. 



Var. stauroneiformis. Median strife entirely absent. 



N. gibba KutZ. (Bac. pi. 28, f. 70 ; H.V.H. Atl. Supp., f. 12*, .Type 

 No. 64), plate 2, fig. 88. 



Differs from the preceding by the median inflation, which is prolonged, 

 while infmitesimally diminishing up to the terminal inflations. Costse about 

 12 in 1 c.d.m., sometimes absent in the median portion. Length, 5 to 7 c.d.m. 



Fresh water. Eegenhoven near Louvain (P. Gaut.). Found throughout Europe. 



Var. brevistriata. (H.V.H. Atl., pi. 6, f. 5*), plate 2, fig. 89. 

 Costse very short, occupying only the margins of the valve. 



Mixed with the type form. 



N. bicapitata Lagerstedt. (D. from Spitsb , n. 6, p. 23 ; H.V.H. 



Atl., pi. 6, f. 14*), plate 2, fig. 90. 



Valve narrow, linear, with apices attenuated, rostrate-capitate ; costse rather 

 fine, 9 to 10 in 1 c.d.m., radiate in the middle of the valve, convergent at the 

 apices, leaving round the raphe a narrow hyaline zone, which expands into 

 a sub-quadrangular area round the central nodule. Length, about 6 c.d.m. 



Fresh water. Not yet found in Belgium. England, Ireland. 



